Internal combustion engines used in automobiles, light trucks and sport utility vehicles, and, particularly those engines fueled by gasoline, inherently produce a loud and irritating roar through the engine exhaust during operation that requires muffling to be bearable to one's ears and, of course, to be legal. Even so, the external noise becomes particularly loud and irritating when the gas pedal is quickly depressed to force the engine to rapidly accelerate to a high rpm. Modern vehicles include the catalytic converter for environmental protection reasons. That device fits in the exhaust system between the engine and muffler and mitigates the exhaust noise slightly, but not significantly. Most factory installed mufflers do the legally required job of dampening the sound to legal levels. What enthusiasts prefer is to convert the sound to a soft melodious sound called the performance sound without robbing the engine of some performance.
During the exhaust portion of the four-stroke engine cycle that follows combustion of the fuel and air mixture that's confined in the engine cylinder, the cylinder exhaust valve associated with an engine cylinder opens and the piston, being moved upwardly in the cylinder toward the exhaust valve, forces the products of combustion from the cylinder. Typical internal combustion engines contain multiple engine cylinders, four, six or eight cylinders, as example. Each cylinder in the engine is “fired” in serial order during the associated compression stage for the cylinder. Once fired, the resulting gaseous products of combustion are exhausted from the cylinder during the succeeding exhaust stage. The repetitive expulsion of the hot exhaust gases forced from each engine cylinder, in turn, and the rapid expansion of those gases into the exhaust manifold of the engine generates noise that is in part periodic in nature. The hot exhaust gas empties into the exhaust manifold and thence flows into the exhaust runners to the exhaust muffler, or, if the vehicle contains a catalytic converter, the metal tubes leading to the catalytic converter, and from the catalytic converter and thence through the exhaust muffler. In either arrangement, from the exhaust muffler the exhaust gas empties into the tailpipe and, thence, to the exterior atmosphere, where the exhaust gas is expelled and the sound is broadcast. With multiple engine cylinders, the foregoing exhaust action of engine operation produces a periodic series of gas pressure pulses and the repetition rate of those pulses varies as a function of the engine rpm. Typically, that pulse rate lies within the audio frequency range.
A typical exhaust muffler provided on the gasoline fueled automobiles of major automobile manufacturers, the OEM muffler, contains several perforated pipes housed within a closed chamber. One of those pipes, the inlet pipe, empties into a front chamber within the housing or casing, while the second pipe provides an exit from a rear chamber. A resonator chamber located at the front of the housing, but behind the front chamber, is also coupled by a pipe or passage to the rear of the front chamber. The resonator contains a specific volume of air and has a specific length that is calculated to produce a sound wave that cancels out a certain frequency of sound. Sound reduction in the muffler relies upon the sound cancellation produced by having reflected and direct portions of the exhaust gas pulse combine in opposite phase inside the muffler so that the sound released through the tailpipe is reduced in level.
Because the pulses of exhaust gas introduced into the muffler must pass through the inlet pipe and exit against a wall in the first chamber and thence return to the middle chamber, one effect of the presence of that barrier wall is to produce a back-pressure at the inlet. Although the OEM muffler sufficiently dampens the harsh sounds produced at the outlet of the tailpipe, the obstruction created by the chamber wall inside the muffler housing produces a back pressure in the exhaust path from the manifold. To overcome the effect of that back pressure, the engine must perform extra work to pump out the exhaust gas. In effect, the back pressure robs the engine of some amount of horsepower that could otherwise be obtained from the engine if the exhaust gas were exhausted directly to the atmosphere without obstruction.
To reduce that back pressure and increase the available horsepower from the engine, performance mufflers were introduced as an after-market product to replace the OEM muffler. Serious performance aficionados could then replace the original equipment muffler with a performance muffler and achieve both better performance and a more desirable sound from the tailpipe.
The OEM mufflers are principally designed to muffle sound. Performance mufflers, on the other hand, are designed not only to muffle the exhaust sound, but also produce a satisfying sound of low frequency and timbre characteristic of performance vehicles. That sound is sometimes referred to as a performance sound. Psychologically, the performance sound gives an audible clue that the vehicle contains great horsepower. Difficult to describe with words and lacking precise definition, the sound may be said to be one that one knows when one hears the sound. As an advantage, the present invention also delivers performance sound.
Performance mufflers previously marketed by others appear to function by one of two basic techniques. One design incorporates fiberglass matting, a sound absorbent material on the outer walls of a perforated tube. The matting absorbs the sound of the resonant audio frequency produced by the exhaust gas as the exhaust gas moves through the perforations in the tube and dampens the sound to tolerable levels within the legal limit. Unfortunately, the matting often breaks down after prolonged use and is discharged into the tailpipe. The matting also absorbs oil and metallic minerals as may be included in the exhaust gases. The accumulation of those substances reduces the sound absorbency of the matting and, hence, the ability of the muffler to absorb or dampen the exhaust sound level. When that occurs, the muffler must be replaced.
The better performance mufflers rely on a chamber single deflector technology which does not require a packing of sound absorbent material. Instead the muffler permits the exhaust gases to flow through the muffler and exit the tail pipe more easily than the OEM packed muffler and produces a lower back pressure. The exhaust gases are directed in a path inside the muffler housing defined by internal metal baffles. Exhaust gas introduced into the performance muffler is directed through internal chambers to the right and the left of the muffler inlet. The foregoing path for the exhaust gas is less restrictive and permits the engine to develop greater horsepower than the absorbent packed muffler, while producing a deep throated rumbling sound desired by many as an advertisement of the power of their automobile engine, often called performance sound. Performance mufflers of the foregoing type have been available for some time from the Flowmaster Company of Santa Rosa, Calif. and variations of that muffler are described in U.S. Pat. No. 4,574,914, U.S. Pat. No. 4,809,812 and U.S. Pat. No. 5,123,502 to which the reader may make reference.
The adaptation of emission controls on automobile internal combustion engines made combustion more efficient and lowered exhaust gas temperatures and catalytic converters were included in the routing of the exhaust gas, all of which aids the effectiveness and/or reliability of an exhaust gas muffler. Although of aid, those additional systems are not for the purpose of muffling engine noise at the exterior and do not do so.
Although solving the problem of exterior noise as might be experienced by a bystander to the vehicle, the muffler should also minimize the engine noise that reaches the interior of the automobile and could be disturbing to the automobile owner. In practice, one finds that OEM mufflers and performance mufflers don't always provide appropriate muffling under all driving conditions. As example, it is found that the internal combustion engine of many sport utility vehicle produces a sound in the interior of the vehicle that is discomforting, if not irritating, that occurs when the engine is operating at about 2200 rpm, which typically corresponds to driving the automobile at a speed of about sixty miles per hour, a typical cruising speed. The engine also produces that annoying sound on acceleration as the engine passes through the 2200 rpm speed. Though the muffler achieves sufficient quietude at other speeds, it appears to produce or allow a resonance inside the vehicle cabin at the 2200 rpm engine speed, which is obviously undesirable.
Then too, when the engine is operating at a high speed above 2200 rpm and the driver removes his foot from the accelerator pedal to allow the vehicle to decelerate, an annoying crackling or “popping” sound is produced inside the cabin that originates at the muffler. That sound is disconcerting to most drivers who may think an engine backfire is imminent. Small pick-up trucks experience a similar problem with cabin sound that the muffler fails to handle when the truck is placed under a heavy load, such as when towing a camper or recreational vehicle, horse trailer or the like.
Muffler durability is also a problem. One finds that some performance mufflers develop hot spots on the muffler case during engine operation. Sometimes the intensity of a hot spot is so great as to produce through localized thermal expansion a bulge in the side of the metal muffler case. That thermal action is likely to lead to a break through in the side of the muffler through which exhaust gases and sound escapes to the exterior. Should that occur, the muffler must be replaced. The foregoing hot spots appear to inherently result from the effect of the baffles located inside the performance muffler, earlier noted. Apparently, a portion of the exhaust gas passing through the muffler is diverted by the internal baffles to create localized vortexes of hot gases in the interior of the muffler. Those vortexes remain stationary in location and don't readily exit the muffler, producing steady heating at a spot on the side of the muffler that, like a blowtorch, ultimately burns through the metal of the muffler case.
Even before any burn-through occurs, the very high temperatures in the performance muffler that are produced by such hot spots often results in driver discomfort or increased fuel consumption. Located on the undercarriage of the vehicle the heat from the muffler is conducted or convected in some measure through the vehicle flooring to the interior of the automobile, which, in the summer, is discomforting to the driver, if automobile air conditioning is unavailable. If air conditioning is available, prolonged operation of the air conditioner is necessary to dissipate the accumulating heat and maintain a comfortable cabin temperature. But prolonged operation of the air conditioner results in greater gasoline consumption, lowering overall engine efficiency.
A performance muffler recently licensed to and marketed by the Edelbrock Corporation, the assignee of the present invention, greatly reduces the potential for such burn-through and vehicle interior heating, while sufficiently dampening engine sound. That is a now patented muffler invented by Mr. Ron Petracek described in a U.S. patent application, entitled “Exhaust Muffler for Internal Combustion Engines,” Ser. No. 10/714,086, and now U.S. Pat. No. 7,044,266, manufactured by Edelbrock Corporation under license. The muffler includes an internal tubular member that contains a louvered cylindrical wall and a number of criss-crossed baffles have an edge positioned facing the incoming stream of exhaust gas, dividing the stream and sound associated with the stream into four parts, leading to the rear of the louvered tube, and another smaller size pair of criss-crossed baffles on either side of the louvered tube with the crossed edges oriented facing an associated small opening in the front circular muffler wall. That muffler has been found to be more effective on diesel engines.
Accordingly, an object of the present invention is to provide an exhaust gas muffler for internal combustion engines.
And, It is a further object of the invention to provide a performance muffler that attenuates the harsh sound of the engine with minimal reduction of engine performance.